public delegate DataGridUpdateDelegate(ref DataGrid datagrid);

public static void DataGridUpdate(ref DataGrid datagrid)
{
    datagrid.Items.Refresh();
}

private void MyDataGrid_Loaded(object sender, RoutedEventArgs e)
{
    ...
    DataGridUpdateDelegate _tmpDelegate = DataGridUpdate;
    _tmpDelegate.BeginInvoke(ref MyDataGrid, nul, null);
}